Optical information storage unit

ABSTRACT

An optical information storage unit and a reader for such a unit are described. The optical information storage unit comprises an information layer and a readout layer. The information layer has a plurality of data areas. Each data area is arranged to emit light when illuminated by light at a predetermined wavelength. The readout layer has a plurality of optical apertures. Each optical aperture is arranged to image substantially the near field of light emitted from a respective data area.

FIELD OF THE INVENTION

The present invention relates to an information storage unit, and inparticular an information storage unit that can be read by an opticalsignal, as well as a reader for the unit, methods of reading from andwriting to the unit, and methods of manufacture of both the unit and thereader.

BACKGROUND TO THE INVENTION

Optical information storage media are relatively inexpensive tomanufacture in terms of the cost per bit of information stored, comparedwith solid state storage devices. The key reason is that the opticalmedia (such as optical disks, including compact discs and digitalversatile discs) are replicable in a one mask process, on a relativelylow cost, plastic substrate.

In comparison, solid state memories typically require a ten maskprocess, and a relatively expensive, defect free, silicon substrate. Dueto the low cost nature of the replication process, optical informationcarriers, such as CD-ROMs (Compact Disc-Read Only Memories), areparticularly suitable for use as publishing media e.g. to distributesoftware, images and/or sound.

Unfortunately, the drives required to read optical media such as opticaldisks are relatively large, consume a large amount of power and arevulnerable to shock and vibration. Consequently, many optical storagesystems use a removable information carrier i.e. the information carriermay easily be separated from the reader device, so as to allow the easydistribution of the low cost carrier.

Various attempts have been made to provide new types of removablestorage medium, which combine the advantages of optical storage(replicability, suitability as distribution medium) with those of solidstate storage units (low power, rapid access, high data rates,relatively robust).

One example of an optical memory card system without moving parts ismanufactured by Ioptics Incorporated, under the product name OROM, anddescribed within U.S. Pat. No. 5,696,714. The product OROM provides a128 MB (Mega Byte) card, measuring 59 mm by 46 mm by 2 mm. The card ismade of a polycarbonate plastic, similar to that used to manufactureCD-ROMs. The data layer is separated into 5000 discrete data patches,each contains 32 kB of data. Micro-diffractive lenses are molded into aplastic lens array, each lens aligned with a respective data patch. Aselection mechanism is utilized to image a specific data patch onto animage sensor.

Whilst the OROM system has the advantage that it has no moving parts,the imaging system is relatively bulky, and the card is relatively largefor the information storage capacity it provides.

Multi-layer card systems have been proposed, in which laser beams areselectively coupled to individual layers, utilizing total internalreflection to guide the laser light to a selected layer, micro-hologramsto selectively couple light out of the layer, and with the resultingbeams being imaged onto an image sensor. However, a multi-layer card isdifficult to manufacture, and thus would be relatively expensive.Further, the addressing and selection of an individual layer is usuallyquite problematic, and is likely to result in relatively expensivereader devices.

It is an aim of embodiments of the present invention to provide anoptical information storage system that addresses one or more of theproblems of the prior art, whether referred to herein or otherwise.

It is further an aim of embodiments of the present invention to providean optical information storage system that provides a relatively highinformation storage capacity per unit area.

STATEMENTS OF THE INVENTION

In a first aspect, the present invention provides an optical informationstorage unit comprising: an information layer comprising a plurality ofdata areas, each data area being arranged to emit light when illuminatedby light at a predetermined wavelength; and a readout layer comprising aplurality of optical apertures, each optical aperture being arranged toimage substantially only the near field of light emitted from arespective data area.

Diffractive effects associated with far field interactions of light withapertures in opaque bodies. By providing a read out layer havingapertures arranged to image substantially only the near field of lightfrom a respective data area, the diffractive effects can besubstantially ignored. Hence the area of each data area can be decreased(and may be even less than the wavelength of light) so as to provide arelatively high information storage capacity per unit area. Further, asthe readout layer is positioned so that the apertures image the nearfield of the data areas, this intrinsically leads to a thin storageunit, which does not require a bulky imaging system to be read.

In another aspect, the present invention provides a reader for anoptical information storage unit, the reader being arranged to removablyreceive an optical information storage unit described above, the readercomprising: a light source arranged to provide light at thepredetermined wavelength for illumination of the data areas; and anoptical sensor comprising a plurality of light sensing areas, theoptical sensor being arranged to detect the near field of light imagedby a respective optical aperture.

In a further aspect, the present invention provides an informationprocessing system comprising at least one of: an optical informationstorage unit as described above, and a reader as described above.

In a further aspect, the present invention provides a method of readinginformation from an optical information storage unit, the informationstorage unit comprising: an information layer comprising a plurality ofdata areas, each data area being arranged to emit light when illuminatedby the light at a predetermined wavelength; and a readout layercomprising a plurality of optical apertures, each optical aperture beingarranged to image substantially only the near field of light emittedfrom a respective data area; the method comprising: illuminating atleast one data area with light at the predetermined wavelength; anddetecting the optical intensity of light imaged by the respectiveoptical aperture that corresponds to the illuminated data area.

In another aspect, the present invention provides a method ofmanufacturing an optical information storage unit, the method comprisingthe steps of: providing an information layer comprising a plurality ofdata areas, each data area being arranged to emit light when illuminatedby light at a predetermined wavelength; and providing a readout layercomprising a plurality of optical apertures, the readout layer beinglocated at a distance from the information layer such that each opticalaperture is arranged to image substantially only the near field of lightemitted from a respective data area.

In a further aspect, the present invention provides a method of writingdata to an optical information storage unit, the information storageunit comprising an information layer comprising a plurality of dataareas, each data being modifiable so as to emit light when illuminatedby the light of predetermined wavelength, and a readout layer comprisinga plurality of optical apertures, each optical aperture being arrangedto image substantially only the near field light emitted from therespective data area; the method comprising: selectively modifying atleast one data area so as to emit light at a predetermined intensitywhen illuminated, the predetermined intensity being indicative of theinformation stored by the respective data area.

In another aspect, the present invention provides a method ofmanufacturing a reader for an optical information storage unit, themethod comprising: providing a locator unit arranged to removablyreceive an optical information storage unit as described above;providing a light source arranged to provide light at the predeterminedwavelength for illumination of the data areas of the storage unit; andproviding an optical sensor comprising a plurality of light sensingareas, the optical sensor being arranged to detect the near field oflight imaged by each respective optical aperture of the storage unit.

BRIEF DESCRIPTION OF DRAWINGS

For a better understanding of the invention, and to show how embodimentsof the same may be carried into effect, reference will now be made, byway of example, to the accompanying diagrammatic drawings in which:

FIG. 1 shows a cross sectional view of an information storage systemcomprising an information card and a reader in accordance with a firstembodiment of the present invention;

FIG. 2 shows a plan view of the readout layer of the card shown in FIG.1;

FIG. 3 shows a plan view of the information layer of the card shown inFIG. 1;

FIG. 4 shows a cross sectional view of an information storage systemcomprising an information card and a reader in accordance with a secondembodiment of the present invention; and

FIG. 5 shows a cross sectional view of an information storage systemcomprising an information card and a reader in accordance with a thirdembodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Near-Field Scanning Optical Spectrometry (NSOM), also referred to asScanning Near-Field Optical Microscopy (SNOM), can use a sub-wavelengthaperture (in combination with an optical detector) to image a surface atsub-wavelength optical resolution. The spatial resolution is determinedby the size of the sub-wavelength aperture in the probe tip. Typically,the probe is scanned over a sample by using a combination ofpiezo-electric transducers and stepping motors, to obtain light opticalimages of the surface at sub-wavelength resolution. In other words, theprobe samples only the “near-field” of the light from the surface,rather than the “far-field” light, and thus the resolution of the probeis not limited by diffraction effects associated with the far-field.

The present inventor has realized that, by providing an appropriatestructure, the physics of near-field coupling can be utilized in opticalinformation storage systems to provide a compact, high informationdensity storage unit.

FIG. 1 shows a cross sectional view of a first embodiment of an opticalinformation storage unit 200 within a reader 100.

The information storage unit 200 in this instance is a removable opticalmemory card. The card consists of a sealed but optically transparentcartridge 205 enclosing an information layer 210 and a readout layer220.

FIG. 2 shows a plan view of the readout layer 220, and FIG. 3 shows aplan view of the information layer 210. In FIGS. 2 and 3, the dottedline AA indicates the plane of the cross sectional view shown in FIG. 1.

The readout layer 220 comprises an optically opaque substrate. An arrayof optical apertures (e.g. 222 a, 222 b, . . . 222 h) is provided, theapertures allowing light to be transmitted through the readout layer220.

The information layer 210 in this instance comprises a transparent layer212 overlaid by an optically opaque covering layer 214. The transparentlayer 212 is used to supply mechanical strength to the information layer210, and could be omitted if desired.

In this embodiment, pits or data areas (e.g. 216 a, 216 c, 216 d, 216 f,216 g) are formed at predetermined locations through the opaque layer,thus allowing light to be transmitted through the layer 214 at the pitlocations. In this particular embodiment, the pits or data areas have arange of possible locations, each of the possible locationscorresponding to a position of an aperture 222 within the readout layer220. A binary system is used, such that the presence or absence of a pitat the potential location is used to represent information.

Within the card, the information layer is placed substantially parallelto, but separated from, the readout layer 220. The layers 210, 220 arealigned so that the positions of the apertures 222 are substantiallyaligned with the positions of potential locations of the pits 216 withinthe opaque coating 214.

The reader 100 comprises a light source 110 and an optical sensor 120.The light source 110 can, for instance be a laser or an LED (LightEmitting Diode, or an array of such devices). The light source isarranged to provide light at a predetermined range of wavelengths, or ata single wavelength λ.

It should be noted that in the specification, the term light is used toindicate any Electro-magnetic radiation, including visible light, infrared and ultra violet wavelength ranges. Further, the terms opaque andtransparent are used in the context that the relevant materialssubstantially block or substantially transmit the passage of light atthe relevant wavelengths utilized to read the device.

In this embodiment, the light source 110 provides light at wavelength λover the complete area of a surface of the information layer. Forconvenience, the light 112 is indicated by discrete arrows (112 a, 112b, . . . 112 h) corresponding to the locations of the optical apertures222 within the readout layer 220.

The optical sensor 120 in this embodiment comprises an array of lightsensing areas or pixels. Each light sensing area corresponds to arespective potential position of a pit or data area The image sensorcan, for instance, be either a CCD (Charge Coupled Device) or CMOS(Complimentary Metal Oxide Semi-conductor) optical sensor.

In order to ensure that each optical aperture 222 effectively andpredominantly images the near-field of light transmitted through therelevant pit or data area 216, the readout layer 220 is separated fromthe opaque layer 214 by a distance δ, where δ<λ. Spacers may be usedwithin the card 205 to maintain this separation. Each of the n×m arrayof transparent apertures 222 (where n and m are integers) are alsodimensioned (i.e. have a width, length or diameter) to be less than thewavelength of the light that will be emitted from the data areas 216(which in this instance corresponds to the same wavelength as theilluminating light 112), and is preferably of similar size to theseparation δ between the layer. Preferably, each of the pits or dataareas is also of width (or, if the data areas are circular, diameter)less than λ.

The spacing of the apertures 222 is chosen to be identical to the pixelpitch W of the image sensor. In typical CCD devices, the pixel pitch isof the order of several micrometers. The spacing d between the cartridge205 and the image sensor 120 is chosen to be large enough to allow thecard to be removable from the reader. Preferably, the readout layer 220is an integral bottom portion of the cartridge, so as to minimize thethickness of the cartridge 205.

When being read, light is transmitted from the light source 110 towardsthe card 205. At the locations where the data areas or pits are formedin the opaque layer 214, light is transmitted through the layer, and thenear-field of this light subsequently imaged by the relevant opticalaperture 222, with the resulting optical signal from the opticalaperture 222 (e.g. 118 a, 118 c, 118 d, 118 f & 118 h) being detected bythe relevant pixel 122 of the image sensor 120.

The image sensor 120 can thus detect, by determining the light intensityincident on a relevant pixel, whether an optical pit exists in thecorresponding position in the opaque layer 214.

It will be appreciated that the above embodiment is described by way ofexample only, and that various alternatives will be apparent to theskilled person as falling within the scope of the present invention.

For instance, the optical sensor may be of substantially the same sizeas the readout layer. However, alternatively a smaller image sensor canbe utilized, and the data read by using stepping means to sequentiallymoving either the card 205 or the sensor 120, so that the sensor scansdifferent portions of the card.

In the above embodiment, the information storage unit 200 has beendescribed as a removable card 205. However, it will be appreciated thatthe information storage unit need not be removable from the reader, butrather the reader could form an integral part of the information storageunit if desired.

In the above embodiment, each data area corresponds to a pit within theopaque covering layer, with the presence or absence of a pit at alocation indicating the information. However, a range of otherembodiments would fall within the scope of the present invention. Forinstance, pits of different sizes (i.e. width, lengths or diameters)could be used to provide a grey-scale, such that different levels oflight intensity received at the detector (corresponding to thedifferently sized pits) indicate different information.

As an alternative to an opaque layer with empty pits, as indicated inFIG. 4, the information layer 214 may contain a fluorescent dye in anarray of pits (216′a, 216′b, 216′c etc). In such an instance, the lightsource 110 would be arranged to provide light at a wavelength λ₁sufficient to excite the fluorescent material. As the materialfluoresces, it would emit light at a longer (lower energy) wavelengthλ₂. This longer wavelength light λ₂ would be detected by the imagesensor 120, once the near-field of the emitted light had been imaged bythe respective optical aperture. In such an instance, the separationbetween the layers 210 and 220 should be less than the wavelength of theemitted light i.e. less than λ₂. Information could again be stored byvarying the presence and/or size of the pits, or the concentration offluorescent material in each pit.

Alternatively, instead of using pits, each data area could correspond toa small reflector. The information layer 210 could be illuminated fromthe side i.e. from the direction parallel with the planar surface of theinformation layer. The apertures in the readout layer would be arrangedto image the near-field of the reflected light from a respectivereflector. The presence or absence of the reflected light would againindicate the relevant information.

As shown in FIG. 4, as an enhancement to any of the embodiments of thepresent invention, the gap between the information layer 210 and thereadout layer 220 could be filled with a material 230 with a refractiveindex at the emitted wavelength (i.e. λ or λ₂) greater than 1. Use of amaterial having a refractive index, n>1 allows the use of even smallerapertures and pits, without a loss of transmission efficiency, therebyenabling higher information densities on the information layer.

The information can be written to the information layer upon manufactureof the information storage unit (200, 200′). Alternatively, writingmeans can be provided to write information to the information layerwhilst in situ, by providing data areas that have optical propertiesthat can be modified by a predetermined process. For instance, data areaon the information layer could be modifiable using similar processes tothat used to write to writeable and rewriteable CD-ROMs.

FIG. 5 illustrates a cross sectional view of a card and a reader inaccordance with a third embodiment of the present invention.

It will be observed that the card 1200 comprises an information layer1210 and a readout layer 1220. As previously, the information layer 1210comprises a transparent layer 1212 and an optically opaque layer 1214.

The reader 100 comprises a light source 110 and an optical sensor 120.The optical sensor comprises an array of light sensing areas, each areabeing of width W.

The readout layer comprises a plurality of apertures (1222 a, 1222 b,1222 c, . . . ), with one aperture per width W of the readout layer. Inthis particular embodiment, the overall width of the optical sensor 120is the same as the overall width of the readout layer 1220, such thateach aperture in the readout layer corresponds to a respective lightsensing area (122 a, 122 b, 122 c, . . . ) of the optical sensor 120.

The significant difference between this particular embodiment and theprevious embodiment is that there are a plurality of data areas 1216 a,1216 b, 1216 c for each aperture 1222 in the readout layer 1220. Theapertures in the readout layer are of a similar size to the data areas.Preferably the spacing δ is slightly smaller than this size, to avoiddifferent apertures in the readout layer simultaneously imaging the samedata area. Preferably, the size (i.e. width, length, or diameter) of thedata areas, the size of the apertures in the readout layer and theseparation between the readout layer and the information layer are allof the order of or slightly smaller than, the wavelength, such that thedevice operates in the near-field coupling regime.

In this particular embodiment, the information layer 1210 is moveablerelative to both the readout layer 1220 and the image sensor 120. Thiscan be achieved by holding the information layer stationary, and movingboth the readout layer 1220 and the optical sensor 120, or morepreferably by holding the readout layer 1220 and the optical sensor 120stationary, and moving the information layer 1210 within a planeparallel to the readout layer 1220 (e.g. within the direction indicatedby the arrows X).

This movement will cause the apertures 1222 to image different dataareas, and consequently the light sensing areas to detect light fromdifferent data areas. For instance, initially, the alignment of the dataareas with the apertures of the readout layer could be such that dataarea 1216 b is imaged by aperture 1222 a, with the light from theaperture being detected by the corresponding light sensing area 122 a.However, if the information layer 1210 is moved slightly to the left,then aperture 1222 a will image data area 1216 c (and again, thecorresponding light sensitive area 122 a detects the light imaged by thecorresponding aperture 1222 a).

This movement can be achieved by movement means, such as apiezo-electric actuator, which can be within the card, but is morepreferably within the reader.

Preferably, the data areas are spaced an integral fraction of thespacing of the apertures in the readout layer. In the embodiment shownin FIG. 5, there is one aperture per distance W in the readout layer,and so there are correspondingly l data areas per distance W in theinformation layer 1210, where l is any integer (and in this particularexample, l=4). Assuming that the data areas 1216, the apertures 1222,and the light sensing areas 122 are regularly spaced, this will allowinformation to be collected in parallel from the data areas by theoptical sensor.

For instance, in the example shown in FIG. 5, if the first data area1216 a is being imaged by the first aperture 1222 a, and detected byoptical sensing area 122 a, then the fifth data area 1216 e willsimultaneously be imaged by the second aperture 1222 b and detected bycorresponding optical sensor area 122 b, the ninth data area alignedwith the third aperture 1222 c etc. Thus, by transversely moving theinformation area 1210 by a distance W (such that data areas 1216 a, 1216b, 1216 c and 1216 d are in turn imaged by readout aperture 1222 a) allof the data areas can be scanned by a respective readout aperture andthe corresponding light sensing area.

In this above example, only a line of data areas/light sensing areas andapertures has been considered. However, assuming that a regular 2D arrayof such apertures, data areas and light sensing areas exist, each lyingwithin the x-y plane, then simply by moving the information layer 1210in the x plane by a distance W and successively in the y plane by adistance W/n for n times, it is possible to scan all of the data areasin the information layer 1210.

It will be appreciated that a reader as herein described, or aninformation storage unit incorporating such a reader, could be utilizedin any information processing system i.e. in any device in whichinformation might need to be written to a storage unit, or read from astorage unit. For instance, such information processing systems wouldinclude computers, music playing systems, image reproducing systems,data storage systems etc.

By providing an optical information storage unit in which the readoutlayer is arranged to allow imaging substantially only of the near-fieldof light emitted from a respective data area, diffraction effectsassociated with the far-field interaction of light from the data area donot occur, and thus a high density information storage unit can beformed. Further, as the imaging of the near-field of light intrinsicallymeans that the readout layer is positioned in close proximity to theinformation layer (i.e. without a convoluted optical imaging path), thena compact optical storage unit can be formed.

1. An optical information storage unit comprising: an information layercomprising a plurality of data areas, each data area being arranged toemit light when illuminated by light at a predetermined wavelength; anda readout layer comprising a plurality of optical apertures, eachoptical aperture being arranged to image substantially only the nearfield of light emitted from a respective data area.
 2. An informationstorage unit as claimed in claim 1, where both the readout layer and theinformation layer are planar and substantially parallel, the separationbetween the information layer and the readout layer being less than thewavelength of emitted light.
 3. An information storage unit as claimedin claim 1, wherein the information layer is movable within a planesubstantially parallel to the readout layer.
 4. An information storageunit as claimed in claim 1, wherein said information layer has a dataareas per unit area, and said readout layer has b optical apertures perunit area, where a>b.
 5. An information storage unit as claimed in claim1, wherein each data area comprises an optical aperture, the lightemitted from each data area when illuminated corresponding to lighttransmitted through the aperture.
 6. An information storage unit asclaimed in claim 1, wherein each data area comprises a reflector, thelight emitted from each data area comprising light reflected from thereflector when the respective data area is illuminated.
 7. Aninformation storage unit as claimed in claim 1, wherein each areacomprises a fluorescent material, the light emitted from each data areacomprising the light emitted by the material as it fluoresces, theilluminating light acting to excite the fluorescent material.
 8. Aninformation storage unit as claimed in claim 1, wherein an opticallytransmissive material is placed between the information layer and thereadout layer, the optically transmissive material having a refractiveindex greater than 1 at the wavelength of the emitted light.
 9. Anoptical information storage unit as claimed in claim 1, wherein at leastone of said data areas is modifiable by a predetermined process so as toalter the optical characteristics of the data area such that theintensity of light emitted by the data area when illuminated will bealtered.
 10. An information storage unit as claimed in claim 1, the unitfurther comprising: a light source arranged to provide light at thepredetermined wavelength for illumination of the data areas; and anoptical sensor comprising a plurality of light sensing areas, theoptical sensor being arranged to detect the near field of light imagedby each respective optical aperture.
 11. A reader for an opticalinformation storage unit, the reader being arranged to removably receivean optical information storage unit as claimed in claim 1, the readercomprising: a light source arranged to provide light at thepredetermined wavelength for illumination of the data areas; and anoptical sensor comprising a plurality of light sensing areas, theoptical sensor being arranged to detect the near field of light imagedby a respective optical aperture.
 12. A reader as claimed in claim 11,further comprising writing means arranged to controllably alter theoptical properties of the data areas, so as to write data to the dataareas.
 13. A reader as claimed in claim 11, further comprising movementmeans arranged to move the position of the information layer relative tothe position of both the readout layer and the optical sensor.
 14. Aninformation processing system comprising at least one of: an opticalinformation storage unit as claimed in claim
 10. 15. A method of readinginformation from an optical information storage unit, the informationstorage unit comprising: an information layer comprising a plurality ofdata areas, each data area being arranged to emit light when illuminatedby the light at a predetermined wavelength; and a readout layercomprising a plurality of optical apertures, each optical aperture beingarranged to image substantially only the near field of light emittedfrom a respective data area; the method comprising: illuminating atleast one data area with light at the predetermined wavelength; anddetecting the optical intensity of light imaged by the respectiveoptical aperture that corresponds to the illuminated data area.
 16. Amethod of reading information from an optical information storage unitas claimed in claim 15, the method further comprising the step of:moving the information layer within a plane substantially parallel tothe readout layer, such that an optical aperture previously imaging afirst data area images a second, different data area within theinformation layer.
 17. A method of manufacturing an optical informationstorage unit, the method comprising the steps of: providing aninformation layer comprising a plurality of data areas, each data areabeing arranged to emit light when illuminated by light at apredetermined wavelength; and providing a readout layer comprising aplurality of optical apertures, the readout layer being located at adistance from the information layer such that each optical aperture isarranged to image substantially only the near field of light emittedfrom a respective data area.
 18. A method of writing data to an opticalinformation storage unit, the information storage unit comprising aninformation layer comprising a plurality of data areas, each data beingmodifiable so as to emit light when illuminated by the light ofpredetermined wavelength, and a readout layer comprising a plurality ofoptical apertures, each optical aperture being arranged to imagesubstantially only the near field light emitted from the respective dataarea; the method comprising: selectively modifying at least one dataarea so as to emit light at a predetermined intensity when illuminated,the predetermined intensity being indicative of the information storedby the respective data area.
 19. A method of manufacturing a reader foran optical information storage unit, the method comprising: providing alocator unit arranged to removably receive an optical informationstorage unit as claimed in claim 1; providing a light source arranged toprovide light at the predetermined wavelength for illumination of thedata areas of the storage unit; and providing an optical sensorcomprising a plurality of light sensing areas, the optical sensor beingarranged to detect the near field of light imaged by each respectiveoptical aperture of the storage unit.